I wish to disable support for JavaScript embedded in HTML-formatted emails in Thunderbird. What is the recommended way of doing this?

In case no one else has this issue, I've been using Thunderbird since the elder days, when it was called Netscape Mail & Newsgroups, and upgrading it all this time; I think JavaScript in email may have been enabled by default way back then.

I found the about:config screen from the Advanced tab in Preferences. There's a very obvious-looking option called javascript.enabled currently set to true. Does this option control running embedded JavaScript in email, and nothing else? In other words, if I disable it, will embedded JavaScript not run, and/or will certain Thunderbird features suddenly stop working? (I'm afraid to try it, because for all I know, the about:config screen is implemented in JavaScript, and there might be no way to return to the screen if I turn it off.)

  • Have I answered your question or does anything remain unclear?
    – Senkaku
    Sep 25, 2015 at 11:38

1 Answer 1


There is a very good article about JavaScript in Thunderbird on ghacks.net, that cites Mozilla.

The main aspects of the article are:

  • With version 3 of Thunderbird Javascript has been disabled completely in message content of emails. There was a javascript.allow.mailnews entry in about:config, that became without effect in version 3 and got finally removed. Look it up in your about:config, it is gone. (Official announcement)

  • JavaScript remains active for remote content of RSS feeds. javascript.enabled is only meant to deactivate JavaScript in RSS and has no effect on your mail, as it is disabled there without option.

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